1. Field of the Invention
The present invention relates to a communication system and a communication device, particularly to a communication system having a plurality of communication devices each of which is connected to a plurality of communication lines, and a communication device composing the communication system.
2. Description of the Related Art
There are various types of communication systems used for conducting communications among a plurality of communication devices. One well-known type of communication system among them consists of a plurality of communication devices each of which is connected with a plurality of communication lines. In such a communication system, the plurality of communication devices conduct serial communications with one another by sending and receiving data when a clock signal that has been sent from one of the devices is received by the rest of the devices. In this system, in general, for the communication device that sends the clock signal, the time at which the clock signal is sent is determined as a reference timing (transmission/reception reference) for sending and receiving data, while for the communication devices that receive the clock signal, the time at which the clock signal is received is determined as the reference timing (transmission/reception reference) for sending and receiving data. Therefore, there is a time delay between the time at which the clock signal is sent from the communication device and the time at which the clock signal is received by the other communication devices, which causes a time lag among the communication devices in their transmission/reception reference.
When the time lag in their transmission/reception reference becomes significant, data may fail to reach a communication device when the device is ready to read the data, or the communication devices fail to synchronize with one another. In order to overcome this problem, such a communication system has been disclosed in Japanese Unexamined Patent Publication No. 1999-068862 that is provided with a correction circuit which is adapted to correct the time lag in the transmission/reception reference.
However, this communication system has to include the correction circuit that is an unneeded component for the purpose of conducting communications in the communication system. Thus, such a circuit causes the communication system to become bulky, and increases the manufacturing cost of the system.